Local defects enhanced dehydrogenation kinetics of the NaBH4-added Li–Mg–N–H system

Abstract

A mechanistic understanding on the enhanced kinetics of hydrogen storage in the NaBH₄-added Mg(NH₂)₂-2LiH system is provided by carrying out experimental investigations associated with first-principles calculations. It is found that the operating temperatures for hydrogen desorption of the Mg(NH₂)₂-2LiH system are reduced by introducing NaBH₄, and the NaBH₄ species seems almost unchanged during dehydrogenation/hydrogenation process. First-principles calculations reveal that the presence of NaBH₄ in the Mg(NH₂)₂-2LiH system facilitates the formation of Mg vacancies in Mg(NH₂)₂. The appearance of Mg vacancies not only weakens the N–H bonds but also promotes the diffusion of atoms and/or ions, consequently resulting in the improvement of the reaction kinetics of hydrogen desorption/absorption of the NaBH₄-added Mg(NH₂)₂-2LiH system. This finding provides us with a deep insight into the role played by NaBH₄ in the Li–Mg–N–H system, as well as ideas for designing high-performance catalysts for metal–N–H-based hydrogen storage media.